PENNSYLVANIAN BRYOZOANS OF EXCEPTIONAL PRESERVATION FROM THE BUCKHORN ASPHALT QUARRY, OKLAHOMA

The Pennsylvanian (Desmoinesian–Virgilian) Buckhorn Asphalt Quarry (Boggy Formation, Deese Group) in Oklahoma, USA is well-known for its exceptional preservation of a diverse fauna of marine invertebrates. The fossils show original shell material, microscopic shell characters and color patterning. Preservation is exceptional because of early impregnation by hydrocarbons that soaked into the sediments and fossils. Results from a new study focusing on the Buckhorn bryozoans are presented here. Nine species of nine genera are recognized; two species (Stenophragmidium buckhornensis and Streblotrypa (S.) heltzelae) are known only from this locality, and two genera (Shishoviclema and Shulgapora) are new to North America. Some skeletal characters that are usually lost during diagenesis are uniquely preserved or are seen for the first time in Paleozoic bryozoans. Preservation of small to large (5–50 µm diameter), node-like surface expressions of styles is pristine. ‘Nanoperforations’ observed in S. (S.) heltzelae, S. buckhornensis and Rhombocladia delicatula are tiny holes (0.5 µm diameter), countersunk into the laminated skeletal walls. Such structures are unknown from other bryozoans (recent or fossil) and their genesis is unclear – were they produced by small-sized symbionts (bacteria?), microendoliths or the bryozoans themselves? The most likely hypothesis is that they were formed by symbionts that lived embedded in the growing walls of the bryozoan zooids. In fractured branches of S. (S.) heltzelae, closely spaced bands of granules are present on the internal walls of the autozooids. Again, such structures have not been observed elsewhere and their origin and function are enigmatic. Mural spines (of varied size and morphology depending on the genus) are reported from R. delicata and Stenoporella sp. Hemiphragms bearing inwardly directed spines 3-30 µm in length are new features of unknown function found in some trepostomes. Finally, a fabric of transverse fibres found in the fenestrate Septopora blanda is reminiscent of a common microstructure seen in post-Paleozoic cyclostome bryozoans but not previously reported in Paleozoic bryozoans.